The present invention relates to innovative polyurethaneurea solutions which can be used for producing hydrophilic coatings on a very wide variety of substrates.
Particularly in the medical sector, hydrophilic coatings on surfaces of medical devices are important since their use can be greatly improved as a result. The insertion and displacement of urinary or blood-vessel catheters is made easier by the fact that hydrophilic surfaces in contact with blood or urine adsorb a film of water. This reduces the friction between the catheter surface and the vessel walls, and so the catheter is easier to insert and move. Direct watering of the devices prior to the intervention can also be performed in order to reduce friction through the formation of a homogeneous water film. The patients concerned experience less pain and the risk of injuries to the vessel walls is reduced by such measures. Furthermore, when catheters are being used, there is always the risk of formation of blood clots. In this context, hydrophilic coatings are generally considered to be useful for antithrombogenic coatings.
Suitable in principle for producing such surfaces are polyurethane coatings which are produced starting from solutions or dispersions of corresponding polyurethanes.
For instance, U.S. Pat. No. 5,589,563 describes the use of coatings having surface-modified end groups for polymers that are used in the biomedical sector, and these coatings can also be used to coat medical devices. The resulting coatings are produced starting from solutions or dispersions, and the polymeric coatings comprise different end groups, selected from amines, fluorinated alkanols, polydimethylsiloxanes and amine-terminated polyethylene oxides. As a coating for medical devices, however, these polymers do not have satisfactory properties, particularly as regards the required hydrophilicity.
A disadvantage of aqueous dispersions of the kind described in publications including U.S. Pat. No. 5,589,563, moreover, is that the size of the dispersed particles makes the coatings relatively rough. Furthermore, the resulting coatings from aqueous dispersions generally lack sufficient stability. Consequently, there is a need for hydrophilic coating systems which exhibit outstanding hydrophilicity in conjunction with a relatively smooth surface and a high stability.
Polyurethane solutions per se are known from the prior art, but—with the exception of the aforementioned polyurethane solutions of U.S. Pat. No. 5,589,563—have not been used for coating medical devices.
Thus, for example, DE 22 21 798 A describes a process for preparing stable and lightfast solutions of polyurethaneureas from prepolymers with terminal isocyanate groups and diamines in solvents of low polarity, by reacting prepolymers of                a) substantially linear polyhydroxyl compounds having molecular weights of about 500 to 5000,        b) if desired, dihydroxy compounds of low molecular weight, and        c) aliphatic and/or cycloaliphatic diisocyanates, the molar ratio of hydroxyl to isocyanate groups being between about 1:1.5 and 1:5,        
in a solvent (mixture) of optionally chlorinated aromatic and/or chlorinated aliphatic hydrocarbons and primary, secondary and/or tertiary aliphatic and/or cycloaliphatic alcohols with diamines as chain extenders, at least 80 mol % of the chain extender being 1,4-diamino-cyclohexane with a cis/trans isomer ratio of between 10/90 and 60/40. These polyurethaneurea solutions are used for producing lightfast films and coatings.
Furthermore, DE 22 52 280 A describes a process for coating textile substrates by the reverse method with adhesion coats and top coats comprising solutions of aliphatic, segmented polyurethane elastomers, which are polycarbonate-containing.
Furthermore, EP 0 125 466 A describes a process for the multiple reverse coating of textile substrates, preferably in web form, for producing synthetic leather, from at least one top coat solution and at least one adhesion coat solution on the basis of polyurethanes.
European Application No. 08153055.2, unpublished at the priority date of the present specification, discloses hydrophilic coatings of polyurethaneureas which are based on a specific combination of polycarbonate polyols as synthesis components and copolymers of ethylene oxide and propylene oxide as end groups.
It has now been found that the mechanical properties of these coatings can be improved by using in the polycarbonate polyol component according to European Application No. 08153055.2, unpublished at the priority date of the present specification, polycarbonate polyols which have structural units of the formula (I)
